Try, opening SFM, pressing F11 to go into game mode, press options in the menu of the game mode, go to the video settings, and click advanced then set the High Dynamic Range to none* , disabling it, and press apply, and try loading a map again or restarting SFM to see if it fixed it.

I can load maps and all now but; everytime I get this error, or what I think is an error.This map is missing high dynamic range (HDR) lightmaps. The SFM requires HDR lightmaps to render properly. You can create HDR lightmaps for your map with the hammer or vrad. See the source Developer Wiki for more info.